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June 21, 2010:
Revised: v2.0

ZL2PD Electronic Christmas Tree

Brighten up the ham shack at Christmas with
this electronic Christmas tree. Adapted from a design originally
published in Elektor magazine in December 2007, this design features an
improved PCB and some component changes for better performance.

Introduction

Christmas
time is usually the time for festive decorations including the
traditional tree. I am usually the one who gets to purchase the tree,
and with varying degrees of help, get it home in the car. The most
demanding task is getting the tree standing properly in the right place
in the house. But, once this is completed, the rest of the family join
in to decorate the tree, adding all sorts of colourful decorations,
along with traditional tinsel and sparkling lights. Most years, we also
have a model train and carriages going around the base of the tree on a
short loop of track to add to the overall effect.

Why should the ZL2PD ham shack be any different? I came across an
interesting design for an electronic Christmas tree in Elektor magazine
a few years ago. It described a colourful LED design but suggested
building the circuit on a very boring triangular shaped PCB.

I have a computer controlled milling machine which I use to make some
of my PCBs. This machine opens up a number of options when it comes to
making PCBs in unusual shapes like this. Why not make it more like the
shape of a real Christmas tree?

So, while it was too late to build the circuit for that Christmas, I
had time to make a few changes to the schematic, to design the new PCB
I had in mind with the help of some drawing software for the tree
outline, and to mill out the required PCB. It was all ready in time for
the next festive season.

For those interested in a different kind of Christmas tree, perhaps for
those in tiny apartments without the space for even the smallest
Christmas tree, this PCB design may be the answer.

The Design

A
series of LEDs are connected to selected outputs of a CMOS CD4060
binary counter. The 4060 also has an internal oscillator which is set
by R1, R2 and C1. Output Q4 is a square wave of twice the frequency of
that on output Q5. In turn, this is twice the frequency on Q6.

The 4060
drives the various LEDs directly from six selected output pins.
Selecting six different outputs from the 14-stage binary counter inside
the 4060, three of which are the slowest output frequencies,
results in a semi-random blinking of the LEDs. The PCB layout is also
arranged such that the LEDs are placed to maximize this near-random
light pattern.

The CMOS output stages deliver constant current to the outputs. The
current is highly dependent on supply voltage. This inherent current
limiting allows the LEDs to be directly connected to these outputs
without the need for additional current limiting resistors.

The only disadvantage of this method is that the LEDs are very bright
when the battery is fresh, but this brilliance steadily falls over the
subsequent weeks of use. However, the LEDs will still blink happily
even when the battery is down to the last few volts of life. Amazing.

Note: The IC used in this circuit is a standard CMOS CD4060. Do NOT
attempt to use a 74HC4060 or 74HCT4060 device in this circuit.

Construction

The PCB
I designed lies at the heart of this design. In my prototype, it stands
about 100mm high. Without access to a CNC milling machine, you will
have to make the PCB using a small hacksaw and a file. With care, it’s
possible to do, but it will take a bit of time.

I purchased a variety of different coloured high-efficiency LEDs from
my local parts supplier. The suggested layout is shown opposite. I
managed to find bright blue, green, red and yellow LEDs, and the
arrangement I used is shown in the diagram at the top of the page. My
supplier had some incredibly bright blue LEDs, and one of those looked
great at the very top of the tree where the star is usually placed on
the full size version.

These LEDs allowed me to power the circuit from a 9V battery for
several hours on most evenings over the three weeks in December leading
up to Christmas Day. The LEDs are really bright for the first two
weeks, but they gradually dim over the following weeks, and the pace of
the LED flashing slows down, but the battery does last for ages.

I didn’t bother adding a power switch to the board. Something of an
oversight, perhaps, but the battery lasts for so long, it’s almost
unnecessary. I just plug in the battery when needed.